Method and apparatus for manufacturing a rim bed by means of cold forming

ABSTRACT

A method for manufacturing a substantially rotationally symmetric rim bed having a wall thickness varying along the longitudinal axis by means of cold forming, wherein the side walls of a substantially cylindrical metal bed having a substantially constant wall thickness are flared radially outwards in a pressing operation, and wherein the wall thickness of the flared side walls is varied along the longitudinal axis by means of flow-spinning, with axial stretching and profiling of the sides. The invention further relates to an apparatus for manufacturing a rim bed by means of cold forming.

The invention relates to a method for manufacturing a substantiallyrotationally symmetric rim bed having a wall thickness varying along thelongitudinal axis by means of cold forming.

Such a method is known from WO 2004/035243 and is used for manufacturinga so-called weight-optimized rim bed for a rim for a tire.

In such a weight-optimized rim bed, which is, for instance, used in arim for a passenger car, truck or trailer, the thickness of the rim bedvaries along the longitudinal axis. Then, at different locations alongthe longitudinal axis, the thickness of the rim bed can be chosen suchthat this is just sufficient for absorbing the local loads. Thus, therim bed may, for instance, be chosen so as to be relatively thick nearthe center of its axial length, in order to weld the rim bed there withthe disk of the rim. In the adjacent areas, the thickness of the rim bedcan then, for instance, be chosen so as to be considerably smaller,whereas the thickness closer to the sides of the rim is usually chosenso as to be larger.

In the known method, the cylindrical steel bed is pre-pressed from theoutsides inwards to the center by means of flow-spinning. Here, the moreouter parts of the bed are brought to a nominal thickness and any excessmaterial is brought to the center of the length of the longitudinal axisand the bed is pre-profiled. Then, in a second flow-spinning operation,in two movements, the bed is stretched from the center axially outwardstowards the sides at locations where the thickness of the rim bed needsto be reduced.

Compared to a manufacturing process in which the flow-spinning takesplace after rolling the profile, as described in DE 2647464, too great adeformation of the bed material can be prevented, so that dressing ofthe sides of the rim bed can be prevented.

Over the process described in WO 02/053307, in which, duringflow-spinning, the bed is processed on a cylindrical mandrel, theprocess described in WO 2004/035243 has the advantage that already somepre-profiling occurs.

However, a drawback of the method according to WO 2004/035243 is that itstill is relatively expensive and time-consuming.

Therefore, the invention contemplates a method of the type stated in theopening paragraph, with which, wile maintaining the advantages, thesedrawbacks can be prevented. To this end, the invention provides a methodfor manufacturing a substantially rotationally symmetric rim bed havinga wall thickness varying along the longitudinal axis by means of coldforming, wherein the side walls of a substantially cylindrical metal bedhaving a substantially constant wall thickness are flared radiallyoutwards in a pressing operation, and wherein the wall thickness of theflared side walls is varied along the longitudinal axis by means offlow-spinning, with axial stretching and profiling of the sides.

By using a cylindrical metal bed with sides flared radially outwards,the bed can be pre-profiled, or even finally profiled, in oneflow-spinning step without dressing of the sides being necessary.

Preferably, here, the material of the bed can move freely in feedingdirection. In particular, here, during flow-spinning, the flared sidewalls of the bed can be pressed from a free position onto a mandrel. Inforward flow-spinning in this manner, the material still to be deformedruns clear of the mandrel and does not run against a stop in feedingdirection, which yields a favorable interplay of forces. In particular,a removing operation can be omitted in forming the cylindrical bed intoa brim bed.

In an advantageous manner, during flow-spinning, in a firstflow-spinning step, the bed is pressed down on a mandrel near the centerarea of the length of the longitudinal axis. As a result, the bed can bepositioned well, so that, during further flow-spinning, a high size andform accuracy can be achieved.

In an advantageous manner, during flow-spinning, in a second processingstep, the bed is axially stretched, radially thinned and profiled fromthe center area of the longitudinal axis in two opposite, outwardlydirected movements with radial pressing down on a mandrel.

Here, the flow-spinning is carried out in axially outwardly directedbasic movements from the center area of the longitudinal axis of the bedtowards the respective sides, while the still loose material to beprofiled is pressed down on the mandrel.

If necessary, the pre-profiled, flow-spun bed can also be rolled to arim bed by means of roll forming.

Preferably, radial expansion of the bed only takes place afterflow-spinning or after the profiling step following flow-spinning.

The invention further relates to an apparatus for manufacturing asubstantially rotationally symmetric rim bed having a wall thicknessvarying along the longitudinal axis by means of cold forming, wherein asubstantially cylindrical metal bed having a substantially constant wallthickness is provided with sides flared radially outwards in a pressingoperation, and wherein the wall thickness of the flared sides is variedalong the longitudinal axis by means of flow-spinning, with axialstretching and profiling of the sides. The apparatus is preferablyprovided with a flow-spinning station for profiling and axiallystretching the flared bed with radial pressing down, and with a pressingstation for radially outward flaring of the sides of a cylindrical bed,while the flow -spinning station connects downstream to the pressingstation.

The invention will be explained in more detail with reference to theexemplary embodiment shown in a drawing.

In the drawing:

FIG. 1 shows a flow diagram of a production line for a rim bed accordingto the invention;

FIG. 2A shows a schematic longitudinal cross-section of the flaredcylindrical bed having a thickness substantially constant along thelongitudinal axis;

FIG. 2B shows a schematic longitudinal cross-section of a bed which ispre-profiled by means of flow-spinning on the basis of FIG. 2A, where itis clearly visible that the thickness of the bed varies along thelongitudinal axis 1;

FIG. 3 shows a schematic longitudinal cross-section of a pressingstation for radially outward flaring of the side walls of a cylindricalbed;

FIGS. 4A and 4B show two schematic longitudinal cross-sections of aflow-spinning station during fixing and stretching/profiling the bedwith flared sides, respectively;

FIG. 5A shows a schematic side elevational view of three successive rollformers;

FIG. 5B shows a schematic longitudinal cross-section of a roll former inwhich a pre-profiled bed is profiled; and

FIG. 6 shows a schematic side elevational view of a radial expander.

It is noted that the Figures are only schematic representations of apreferred embodiment of the invention which are given exclusively by wayof non-limiting exemplary embodiments. In the Figures, same orcorresponding parts are designated by the same reference numerals.

FIG. 1 schematically shows a flow diagram for a production line P for arim. In a preparation part 1 of the line, metal strips are cut to lengthin a first step 1.1 and formed into a cylindrical bed in a second groupof steps 1.2. Here, the strip is successively coiled (1.2.1) and itsfront ends are welded to each other (1.2.2), after which the weld isdressed (1.2.3).

In a second part 2 of the line, the cylindrical rim bed having aconstant wall thickness formed in part 1 is formed into a profiled rimbed in a profiling line (2.1) and then tested for leakage and providedwith a valve hole (2.2). The profiling takes place by means of coldforming of the material, i.e. the material is not melted and no removingtakes place. In a first processing station 2.1.1, the side walls of thebed are flared radially outwards to the basic form shown in FIG. 3 in anaxially inwardly directed pressing operation with the aid of mandrels.Then, as will be elucidated hereinafter, in a second processing station2.1.2, the wall thickness of the flared bed is varied along thelongitudinal axis by means of flow-spinning with simultaneouspre-profiling of the bed.

Then, in a third processing station 2.1.3, the pre-profiled bed isprofiled to a rim bed by means of roll formers, after which the profiledbed is radially expanded to the desired size in a fourth processingstation 2.1.4.

After a check for leaks and provision of the valve hole, the rim bed isready to be assembled with the disk to a rim in an assembly part 3 ofthe production line. Depending on the type of rim, the disk is connectedwith the rim bed at a predetermined location along the longitudinalaxis.

In FIG. 2A, a longitudinal cross-section of the flared cylindrical bed10 having a constant diameter along the longitudinal axis is shown.

In FIG. 2B, the pre-profiled bed 20 is shown, while it is clearlyvisible that the thickness t of the bed varies over the length of thelongitudinal axis 1.

In FIG. 4A, the flow-spinning station 2.1.2 is schematically shown.

The flow-spinning station is provided with two rotatably arrangedmandrels 11A, 11B which are each axially slidable along the longitudinalaxis 1 of the flared bed 10. In the Figure, the mandrels 11 are eachplaced from a side 12A, 12B of the flared bed 10 to the center area M ofthe length of the longitudinal axis 1 of the bed. During the sliding inof the mandrels 11A, 11B, the bed is clamped at its sides 12A, 12B withthe aid of slidable stop collars 14.

The flow-spinning station further comprises one or more rollers 13 whichcan move radially with respect to the longitudinal axis of the bed 10and which are further translatable with respect to the longitudinal axisof the bed 10. The rollers 13 are further rotatably arranged withrespect to the flared bed 10. Here, the rollers 13 and/or the flared bed10 can rotate with respect to the fixed world during production.

FIG. 4A shows how, in a first processing step, the flared bed 10 ispressed down on the mandrels 11A, 11B near the center area M of thelength l of the longitudinal axis of the bed 10 in a first flow-spinningstep. The thickness t of the center area M remains substantially equal.

Then, as shown in FIG. 4B, with the aid of the rollers 13A, 13B, thematerial of the bed 10 is moved outwards along longitudinal axis 1 intwo successive, opposite movements with radial pressing down, so that,with axial stretching of the bed 10, the thickness t of the bed 10 islocally reduced.

At the same time, the material of the flared side of the bed 10 ispressed down from the free position on the mandrel 11 by the rollers13A, 13B, so that the side wall of the bed 10 is pre-profiled to thepre-profiled bed 20 shown in FIG. 2B. It is noted that, in the schematicview, the thickness t only varies little over the longitudinal axis 1.It will be clear that, in practice, the thickness variation may begreater or smaller than shown herein. Also, more or fewer areas havingdifferent thicknesses can be formed than shown herein.

During the processing process, the bed material flows outwards withrespect to the center of the longitudinal axis towards the side. Ifdesired, during the second processing step, the sides of the bed 12A,12B can be supported by means of the slidable stop collars 14. FIG. 4B,however, shows that the slidable stop collars do not support the sides12A, 12B.

After processing, the stop collars 14 are again brought into contactwith the sides 12A, 12B, after which the mandrels 11A, 11B are axiallywithdrawn. With axial withdrawal of the stop collars 14, thepre-profiled bed 20 can then be removed.

So, in the second processing step shown in FIG. 4B, from the center, twosuccessive, sideward flow-spinning operations are carried out. It is ofcourse possible to carry out flow-spinning operations from the center toboth sides simultaneously.

It is noted that the invention is not limited to the embodiments shownherein and that many variations are possible within the scope of theinvention as set forth in the following claims.

1. A method for manufacturing a substantially rotationally symmetric rimbed having a wall thickness varying along the longitudinal axis by meansof cold forming, wherein the side walls of a substantially cylindricalmetal bed having a substantially constant wall thickness are flaredradially outwards in a pressing operation, and wherein the wallthickness of the flared side walls is varied along the longitudinal axisby means of flow-spinning, with axial stretching and profiling of thesides.
 2. A method according to claim 1, wherein, during flow-spinning,the flared side walls of the bed are pressed down from a free positionon a mandrel.
 3. A method according to claim 1, wherein, duringflow-spinning, in a first flow-spinning step, the bed is pressed down ona mandrel near the center of the length of the longitudinal axis.
 4. Amethod according to claim 3, wherein, during flow-spinning, in a secondprocessing step, the bed is axially stretched, radially thinned andprofiled from the center area of the longitudinal axis in two opposite,outwardly directed movements with radial pressing down on a mandrel. 5.A method according to, claim 1 wherein the pre-profiled, flow-spun bedis rolled to a rim bed by means of roll forming.
 6. A method accordingto claim 1, wherein the bed is only radially expanded afterflow-spinning and optionally roll forming.
 7. An apparatus formanufacturing a substantially rotationally symmetric rim bed having awall thickness varying along the longitudinal axis by means of coldforming, wherein a substantially cylindrical metal bed having asubstantially constant wall thickness is provided with sides flaredradially outwards in a pressing operation, and wherein the wallthickness of the flared sides is varied along the longitudinal axis bymeans of flow-spinning, with axial stretching and profiling of thesides.
 8. An apparatus according to claim 7, wherein, duringflow-spinning, the flared side walls of the bed are pressed down from afree position on a mandrel.
 9. An apparatus according to claim 8,wherein a pressing station is provided for radially outward flaring ofthe sides of a cylindrical bed.
 10. An apparatus according to claim 8,wherein a flow-spinning station is provided for profiling and axiallystretching the flared bed.
 11. An apparatus according to claim 10,wherein the flow-spinning station connects downstream to the pressingstation.
 12. An apparatus according to claim 10, wherein theflow-spinning station is located upstream of a rolling station forrolling the pre-profiled, flow-spun bed to a rim bed.